Leave car: trade-in arranged (7)
I believe the answer is:
detrain
'leave car' is the definition.
(leave a train carriage or car)
'trade-in arranged' is the wordplay.
'arranged' is an anagram indicator.
'trade'+'in'='tradein'
'tradein' with letters rearranged gives 'DETRAIN'.
(Other definitions for detrain that I've seen before include "Get off at a station" , "leave car" , "get out of carriage" , "leave coach behind" , "leave Orient Express, perhaps" .)